In cutting and grinding processing, cutting and grinding oils have been used in order to extend the working life of tools such as drills, end mills, tool bits, grinding stones and the like, improve the roughness of the finished surface of a workpiece, and improve processing efficiency thereby, resulting in an improvement in the productivity of machining.
Cutting or grinding oils are roughly classified into two types of oils, i.e., water-soluble oils which are put in use after diluting the surface-active agent and lubricant component contained therein with water, and water-insoluble oils which contain a mineral oil as a main component and are used as it is, i.e., in the form of a stock solution. In the conventional cutting and grinding processing, a relatively large amount of a cutting and grinding oil is supplied to processing spots of a workpiece regardless of which type of oil is used.
The most basic and important functions of the cutting and grinding oils are lubricating and cooling properties. Generally speaking, water-insoluble cutting and grinding oils are superior in lubricating properties, while water-soluble ones are superior in cooling properties. Since the cooling properties of the water-insoluble cutting and grinding oils are inferior to that of the water-soluble ones, it is necessary to supply the water-insoluble cutting and grinding oil in large amounts, ranging from several liters to over ten liters per minute.
Cutting and grinding oils which are effective in improving processing efficiency have undesirable aspects, from different viewpoints. The typical examples of such aspects are problems concerning with the environment. Regardless of whether water-soluble or water-insoluble, the oils are gradually deteriorated during the use thereof and finally become incapable of further use. For instance, a water-soluble oil becomes unable to be used when it undergoes the separation of the components or deteriorates the environment in terms of sanitary, caused by deteriorated stability due to the growth of microorganisms. A water-insoluble oil becomes unusable when the acidic components generated with the progress of oxidation make workpieces corrode, or the viscosity is significantly changed. Furthermore, the oil is spent by adhering to metal chips or swarf and becomes wastes.
In such a case, the deteriorated oil is disposed and then replaced with a fresh oil. The oil disposed as wastes is necessarily subjected to various treatments so as to avoid adverse affects on the environment. For instance, cutting or grinding oils which are developed for the primary purpose of improving working efficiency, contain a large amount of chlorine-containing components which may generate harmful dioxin during thermal disposal. Therefore, removal of such components is required. For the reason of this, cutting or grinding oils which are free of chlorine-containing components have been developed. However, even though the oils contain no chlorine-containing component, they would adversely affect the environment, if their waste disposal volume is large. The water-soluble oils may pollute the surrounding water area, and are, therefore, necessarily subjected to highly-developed treatments that require large costs.
The field of manufacturing nonferrous metal parts to be used in automobiles and home electric appliances is cited as one example where it is difficult to achieve both an improvement in cutting and grinding properties and a reduction in burdens on the environment. More specifically, when nonferrous metal parts such as those of aluminum or aluminum alloys are processed, water-soluble oils have been generally used, but the waste oils resulting from the processing often contain metals dissolved therein and thus leads to a problem that disposal of the waste oils entails enormous cost. Further, the use of the water-soluble oils require strict and tedious adjustments in pH because the use of an oil with an inappropriate pH would decompose or cause corrosion on the surfaces of parts.
In the nonferrous metal processing industry, the use of dry processing or water-insoluble oils has been studied in order to solve the foregoing problems.
On the other hand, a minimal quantity lubrication cutting and grinding processing method has been developed to provide a novel processing method. This method is carried out by supplying oil in a trace amount of 1/100000 to 1/1000000 of the amount of oil used for conventional cutting and grinding to processing spots together with a compressed fluid (for example, compressed air). This system can obtain a cooling effect with compressed air and can reduce the amount of wastes due to the use of a minimal quantity of oil, resulting in a reduction in adverse affects on the environment that is caused by large amounts of waste disposal. Therefore, this method has been expected to be used for processing not only nonferrous metals but also ferrous metals or any other metals.
The minimal quantity lubrication system is required to provide a processed product with excellent surfaces even though the amount of oil to be supplied is minimal, to reduce the wear of tools, and to carry out cutting and grinding efficiently. Therefore, the cutting and grinding oil used for the system is required to have high quality properties. The oil is desirously an oil with excellent biodegradability in view of waste disposal and working environments.
In the minimal quantity lubrication system, it is very important to generate excellent oil mist. Oil mist if in poor state causes plugging of piping and thus fails to reach processing spots sufficiently, resulting in the tendency that the cutting and grinding properties are degraded or the working life of tools is shortened. Whereas, if oil is likely misted excessively, it would scatter and pollute the working environment when pumped out. Also in this case, oil mist scatters and thus fails to reach processing spots sufficiently, resulting in the tendency that the cutting and grinding properties are degraded or the working life of tools is shortened.
Further, in the minimal quantity lubrication system, the oil is supplied in the form of mist. Therefore, if an oil with a poor stability is used, the oil likely adheres to the interior of a working machine, a workpiece, the inside of a mist collector and the like, i.e., causes “sticking phenomenon”. As the result, the oil invites a problem in treatability and reduces the working efficiency. Therefore, in the minimal quantity lubrication system, it is desirous to use an oil that unlikely becomes sticky.
In the conventional minimal quantity lubrication cutting and grinding method, it has been common to use a compressed air as a compressed fluid (see WO2002/083823). However, it has been frequently observed that in nonferrous metal processing in particular, processing using a compressed air may not be sufficient in cutting and grinding properties.